The invention relates to a method and to an apparatus for the three-dimensional measurement of objects.
In known methods for the three-dimensional measurement of objects such as workpieces, the objects are positioned on a measuring table at which an apparatus with a measuring element is movably arranged for the scanning of the outer contours of the objects, with the location of the measuring element being able to be determined via linear, three-dimensional transducers in the x, y and z directions. As a rule, the measuring table is a ground, solid block of marble which is usually installed in a stationary manner.
The measuring element consists, for example, of a scanning measuring sphere which is mechanically connected to a force sensor to ensure a continuous contact with the object. On scanning, the measuring sphere is moved into contact with the object and along the object. A computer determines the outer dimensions of the three-dimensional object from the movement of the measuring sphere along the object using the linear transducers which have a precisely fixed location to the measuring table. Other apparatuses with pneumatic feelers, which can also be positioned into the openings of the workpiece, are used for the measurement of inner dimensions.
Such apparatuses for the three-dimensional measurement of objects are very rarely used directly in production halls since, for example, water or oil used there, chips which occur, vibrations which arise and electrical problems can result in measuring imprecision. An additional disadvantage is the relatively low measuring speed due to the linear transducers and the large space requirements due to the solid marble measuring tables.
Special measuring apparatuses are therefore often used in industry which are only optimized for one measuring task, for example for a diameter measurement of a piston. In addition to scanning spheres, electro-pneumatic transformers, capacitive sensors and inductive scanners are used as measuring elements. The workpieces are introduced into the measuring apparatus using a handling system which can have a very complex design. A handling system is furthermore again required for the removal of the workpieces from the measuring apparatus, for example for the classification into usable and non-usable workpieces or workpieces which have to be reworked.
Measuring elements for the scanning of the object are provided, for example, on a crane or a stand for large objects to be measured such as car bodies. The crane or the stand and the object to be measured are movable relative to one another in order to scan the object sectionally with the measuring elements arranged on the crane or on the stand. It is disadvantageous in this process that there is a limitation with respect to the size of the measurable object due to the dimensions of the stand or to the range of the crane. The stand or the crane is moreover usually installed in a stationary manner and can therefore be transported to a different location for the measurement of objects with difficulty.
The measurement of larger objects and spaces therefore very often requires a high effort. Since the measurement of large objects is a point one as a rule, the actual shape of the objects is determined by measurement of a few points and interpolation or extrapolation for cost reasons. This can result in substantial imprecision of the measured data.